A major new study has drawn a direct link between the consumption of ultra-processed foods and fertility, suggesting men who eat more UPFs take significantly longer to get their partners pregnant, while women who consume them may see slower early development of their embryos.
The research, published in the journal Human Reproduction and led by Dr Romy Gaillard, a paediatrician at Erasmus University Medical Center in Rotterdam, analysed the diets of 831 women and 651 men trying to conceive. It found men with the highest intake of UPFs had a 75% greater risk of subfertility, defined as taking 12 months or longer to achieve pregnancy. For the women who conceived, higher UPF consumption was associated with slightly smaller embryonic growth and a smaller yolk sac size by the seventh week of pregnancy—a marker linked to higher risks of miscarriage and premature birth.
Scrutiny of the study’s method and meaning
However, the study’s design and the scale of its findings have led to significant caution from independent experts. The research is observational, meaning it can identify correlations but cannot definitively prove that UPFs cause the fertility issues. As Professor Kevin McConway, an emeritus professor of applied statistics at The Open University, noted, this kind of study is not the medical “gold standard” of a randomised controlled trial.
The primary challenge, experts highlight, lies in untangling the influence of what are known as confounding factors. People who consume a diet high in UPFs often have other lifestyle, socioeconomic, or health characteristics that could independently affect fertility. These can include having a higher body mass index (BMI), lower income, different overall dietary patterns, or higher consumption of alcohol.
The Dutch research team attempted to adjust their figures to account for many of these variables. Despite this, Professor McConway and others argue precise adjustment is exceptionally difficult. Crucially, because the observed effects on embryo size were described as “tiny” and “marginal” by experts, even minor residual confounding could explain the results. “If something was having a massive effect, then I would say: ‘That looks pretty obvious’,” said Dr Channa Jayasena, a fertility doctor at Imperial College London. “But actually, it’s so marginal that it wouldn’t surprise me if another study came out and failed to show that.”
Expert skepticism on changing advice
This statistical uncertainty underpins a strong consensus among commentators that the study alone is not a basis for altering public health guidance. Professor Gunter Kuhnle, a nutritionist at the University of Reading, warned that “making bold claims based on a single observational study is always worrying – especially when the results are likely to cause distress to some people.”
Dr Jayasena expressed particular concern about the potential impact on couples already facing the strain of infertility. “Couples with fertility problems are faced with a barrage of advice from the media. It’s such a stressful time,” he said. He worries that adding a strict avoidance of all UPFs to this “barrage” could be counterproductive, potentially increasing stress or diverting focus from well-evidenced lifestyle changes like stopping smoking. “If you take all the enjoyment out of everything, then it can leave people miserable,” he added, emphasising the importance of balance.
The study is the first to examine the combined impact of both partners’ UPF consumption, and the researchers concluded that a diet low in such foods would be best for chances of pregnancy and foetal health. The experts critiquing the work agree its findings justify further investigation into any potential biological mechanisms, but stress that replication in larger, more diverse populations is needed.
The wider landscape of UPFs and health
The fertility research adds to a substantial and growing body of evidence linking high UPF consumption to a wide spectrum of health problems. Broad scientific reviews have associated these foods, which are typically high in additives, salt, sugar, and unhealthy fats while being low in fibre and whole nutrients, with over 30 adverse conditions. These range from obesity, type 2 diabetes, and heart disease to mental ill-health, certain cancers, and dementia.
In the UK and other high-income nations, UPFs account for more than half of the average person’s calorie intake, making their potential health impact a significant public health question. General dietary advice for those trying to conceive has long emphasised overall healthy patterns, such as the Mediterranean diet, rich in fruits, vegetables, whole grains, and lean proteins. Specific nutrients like antioxidants, folate, and omega-3 fatty acids are known to support reproductive health, while diets high in trans fats and processed meats are linked to poorer fertility outcomes.
Dr Jayasena affirmed that the strength of evidence for traditional, holistic lifestyle approaches remains “phenomenally strong.” His advice to couples focuses on that foundation without prescribing a rigid avoidance of all processed foods. “It is important to reassure couples that in the larger scheme of things, of course it’s good on the whole to be healthy,” he said. “But you’ve got to live as well.”